A technique for growing SiC single crystal from gas as raw material is disclosed in JP-B2-3941727 corresponding to U.S. Pat. No. 7,217,323. A device for manufacturing SiC single crystal in JP-B2-3941727 is shown in FIG. 3.
In the device, a heat coil J2 is arranged around a vacuum chamber J1. The inside of the chamber J1 is vacuumed through a discharge pipe J3. Further, raw material gas J5 for SiC material is introduced in the chamber J1 through a gas introduction pipe J4. Thus, a SiC single crystal ingot J9 is grown on a SiC single crystal substrate J8 as a seed crystal, which is disposed in a reaction chamber J7. The reaction chamber J7 is disposed inside of heat insulating material J6. The raw material gas J5 introduced from the gas introduction pipe J4 is heated and decomposed in a raw material gas heating chamber J10. The heating chamber J10 has a hollow center, and is disposed on an introduction port of the gas introduction pipe J4. The raw material gas J5 is supplied to the substrate J8 through the hollow center of the heating chamber J10. Residual raw material gas, which is not used for the crystal growth, is flown through an opening passage J11, which is provided by clearance between the sidewall of the heating chamber J10 and the inner wall of the reaction chamber J7. Then, the residual raw material gas is discharged through the discharge pipe J3 so that the gas is evacuated to the outside of the vacuum chamber J1.
The ingot J9 has the maximum diameter, which is substantially equal to the inner diameter of the reaction chamber J7.
In the above device, it is necessary to form sufficiently wide opening passage J11 for discharging the residual raw material gas J5. Specifically, the clearance between the inner wall of the reaction chamber J7 and the outer wall of the heating chamber J10 is sufficiently widened. Further, it is necessary to form the sidewall of the heating chamber J10 having the sufficiently large thickness for heating and decomposing the raw material gas J5. Thus, the raw material gas J5 is mainly supplied to the center of the substrate 38, so that the center of the ingot J9 is rapidly grown. Thus, the growth rate at the center of the ingot J9 is larger than that at the periphery of the ingot J9. As a result, the surface of the ingot J9 becomes a convex shape. The diameter of the ingot J9 is smaller than the diameter of the substrate J8, and thereby, the process yield becomes low.
JP-A-2002-154898 corresponding to U.S. Pat. No. 6,770,137 teaches that the inner diameter of the sidewall of the heating chamber J10 becomes larger toward the substrate J9, so that the inner wall of the heating chamber J10 has a tapered surface. Thus, the area, to which the raw material gas J5 is supplied, is widened, and the diameter of the ingot J9 increases.
When the inner wall of the heating chamber J10 has the tapered surface, the position of the inner wall of the heating chamber J10 becomes far from the coil J2 as the position approaches toward the gas introduction pipe J4. Thus, the raw material gas J5 is not sufficiently heated by the coil J2, so that the raw material gas J5 is not sufficiently decomposed.
Thus, it is required to increase the diameter of the ingot and to improve the process yield of the SiC single crystal.